Rifle scopes, also called telescopic sights, were first invented and affixed to long barrel firearms around the late 1830s. Since that time, longarms have improved in manufacturing quality, shooting accuracy, effective range, and hitting power. Recoil force and impulse have also increased not only in military arms but with civilian arms as well.
Firearms, both rifles and pistols, compressed-gas guns, spring-powered rifles and pistols, and others, have been enhanced by optical telescopic sights mounted to the weapon by attachment systems employing split-clamping rings. Such rings historically have clamped around the tubular sections of such telescopes and provide various adapting-clamping systems as part of the ring to complete the attachment of the telescope to the firearm itself.
A recurring problem of the split-clamping ring portion of the mounting is the shifting of the telescope within the clamping ring due to the forces of inertia. Such forces are generated by the recoil of the firearm's discharge, or moving, jarring effects of the various mechanical movements of bolts, slides, heavy springs, etc. If the telescope shifts, the impact point on the target may also shift, degrading the precision and accuracy of the firearm which opposes the purpose of mounting the telescope which is the precision and reliability of projectile placement.
The clamping action of most split-ring type mounts uses friction generated by the clamping force applied by the ring to the smooth, cylindrical telescope body tube. Various approaches have been applied to prevent the shifting of the telescope in the clamping rings, including (a) glue or plastic fillers applied between scope and rings, (b) friction enhancers such as fine sand paper inserts, but mainly (c) the use of larger split-ring clamps able to apply greater clamping forces to keep the scope tube from inertial-dynamic shifting in the rings. These methods have been largely successful at reducing or preventing scope shift in firearms chambered to traditional calibers in service from decades ago to the present time.
However, as interest in extreme long distance and precision shooting increases, modern telescopes are being produced with higher magnifications, which are of larger diameter to let in more light, and are correspondingly more massive. Long range firearms such as those chambered in .338 Lapua, .50BMG and even 20 mm generate much greater recoil than traditional cartridges, and the inertia of a heavier scope subjected to a heavier recoil impulse demand more positive anti-slipping means of attaching a telescopic sight to a rifle.
Another problem encountered by users of firearm mounted telescopic sights encounter is the alignment of the telescope with the firearm's bore: at the time when a scope is mounted the rotational alignment of the scope about the scope's longitudinal axis is established, and once the scope is zeroed-in it is desirable that this alignment not be perturbed.
Although uncommon, some rifles are designed with sighting means that may be both vertically and horizontally offset from the shooting axis of the weapon. However for the vast majority of rifles the reticle in the scope's sight picture should normally be adjusted so when the viewer holds the horizontal reticle level and the vertical reticle perpendicular to level, the centerline of the bore of the firearm should be directly vertically below the intersection of the horizontal and vertical reticles in the scope's sight picture. If this condition is not met the projectile will probably not impact where intended. With traditional friction-type split-ring clamps, this desired alignment can be lost when tightening the clamping screws when installing the scope.
Traveling with scoped firearms presents additional challenges because many components inside the scope are delicate and rely on exceedingly precise adjustments and alignments of small and fine parts. Like other parcels, rifles shipped by common carriers or aboard commercial passenger planes, buses, vessels, or trains are subjected to dropping, kicking, accidental shocks, and sometimes even willful abuse. Despite presenting a more awkward aspect ratio than most other luggage, the barrel, receiver, and stock of firearm secured in a case are generally much more robust than the delicate scope, have a better chance of surviving the transit or shipping undamaged and unscathed. Thus for people traveling with their scoped rifles, there is an interest in being able to detach a scope from the rifle so as to carry it under their own watchful eyes and gentle care.
Besides horizontal and vertical alignment and the demands of secure attachment of a scope to a rifle, a shooter needs to be able to fix the scope onto the rifle at an appropriate distance ahead of where the shooter's head rests when looking through the scope to aim the rifle at a target. Since this ideal distance may sometimes be less than an inch or only a few inches, a gun having heavy recoil can be thrust backward and the rear rim of the scope can strike the shooter in the forehead and even lacerate the skin above the eye pinched between the scope rim and the shooter's skull. The consequence of “scope bite,” as this is called, can range from a minor blunt force inconvenience to a substantial injury including bleeding.